An Analysis of a Numerical Tidal Model Applied to the Columbia River
Abstract
An implicit finite difference model for predicting flood routing is applied to the lower Columbia River, where tidal forcing causes flow reversals interacting with upstream dam flow during small river flow periods. The model is one dimensional, unsteady, including lateral inflow and variable bed friction for different channel sections. A comparison of stages at six station was made for a sensitivity analysis. The analysis used a total of 2209 hours of simulated river stages. Downstream boundary changes of + or - 0.5 feet and + or - 2.0 feet were made to the Astoria tide stages. Model simulations showed that 70% of the tide difference appears at Vancouver and Portland, 80% at St. Helens, 85% at Longview, 93% at Wauna and 95% at Skamokawa. Varying the upstream boundary condition (Bonneville Dam discharges) by + or - 10% and + or - 25% were markedly different from the downstream boundary changes. Upstream, where the tide influence is weakest, the tidal cycle is more likely to be washed out by the higher flows of the Columbia. Also these changes fluctuated with the tide cycle. Downstream stations did not show such differences because of the larger cross section areas of the Columbia River nearer the mouth and the proximity to the downstream boundary condition. The river system was calibrated in a downstream to upstream direction and used a total of 606 hours observed river stages. Three periods with distinct river flow conditions were used in the calibration. Theses.
Document Details
- Document Type
- Technical Report
- Publication Date
- Sep 01, 1988
- Accession Number
- ADA201695
Entities
People
- Richard B. Koehler
Organizations
- Naval Postgraduate School